Crosstalk is a known issue where signals transmitted on one channel, e.g. a data channel, may provide an unwanted contribution to signals on another channels. This can be a concern for multichannel audio signals, and may in particular be an issue where the output transducers share a common ground return, as may typically be the case with removably connectable peripheral apparatus with stereo loudspeakers such as headsets/headphones or the like.
FIG. 1 illustrates one example of a stereo audio system 100. FIG. 1 illustrates two audio signal paths, Left and Right, each path having: a digital-to-analogue converter (DAC) 101 for receiving a respective digital audio signal and producing an analogue signal; and an output driver 102 for producing a respective driving signal VL and VR for a respective loudspeaker 103. The loudspeakers 103 are connected to a common ground return path. This arrangement may be typical when the audio driving circuitry, e.g. DACs 101 and drivers 102 are part of a host electronic device, such as a portable electronic device for example, which in use is connected to a peripheral apparatus such as a headset via a suitable connector such as a jack plug and jack socket (not shown).
This arrangement, which includes the common return path which can be thought of as having a common impedance RC, can lead to unwanted crosstalk talk between the audio channels as will be recognized by one skilled in the art.
One known approach to reducing the crosstalk is to add to each channel a signal component, derived from the signal of the other channel, which is intended to cancel the crosstalk at the loudspeaker. Thus as illustrated in FIG. 1 the signal from the left channel may be tapped and received by gain element 104 which applies a predetermined gain factor ρ before being mixed with the signal in the right channel by mixer 105. Likewise a signal from the right channel is tapped and mixed with the signal in the left channel by mixer 105 after a predetermined gain λ is applied by gain element 104. Conveniently the mixing in both the left and right channels is performed in the digital domain and thus gain elements 104 are digital gain elements. The effect of this mixing adds a deliberate leakage between the two channels that is intended to mitigate the crosstalk at the loudspeakers.
The gain factors λ and ρ are predetermined and are set so as to cancel crosstalk for an expected load impedance and common impedance RC.